Disposal of waste is becoming a serious problem due to the huge volume thereof increasing from year to year. On the other hand, recovering useful constituents from the refuse waste has been considered and several methods and apparatuses have been developed. Usually, constituents of the municipal waste are more or less incinerated for disposal. However, mere incineration may result in loss of some usable constituents and environmental pollution.
Pyrolysis gas may be recovered from organic materials by thermally decomposing or pyrolyzing the same. The pyrolysis gas thus recovered may be utilized for several purposes, for example as fuel, material for producing chemical resources, etc.
Heretofore, several pyrolyzing apparatuses have been used for thermally decomposing the organic refuse to recover pyrolysis gas therefrom and a thermal reactor of a fluidized bed type has been found to be useful to such end.
However, when a thermal reactor of a single fluidized bed type is employed, it is necessary to supply an appropriate amount of heat for maintaining endothermetic reaction by incinerating a part of the organic materials intended to be pyrolyzed for recovering the pyrolysis gas therefrom. Accordingly, pyrolysis gas generated by thermal decomposition or pyrolyzing is diluted or thinned with exhaust gas thereby considerably lowering the calorific content of the recovered gas and, thus, degrading the quality of the recovered pyrolysis gas. Further, carbon adheres to the surface of the inert particles or grains used to form the fluidized bed thereby making it impossible to maintain the condition of fluidized bed substantially stable. Therefore, in order to maintain the preferable condition, grains with carbon adhering thereto must be constantly or periodically removed from the reactor for restoration or regeneration by a separately provided apparatus which adds complexity to a total system and operation.
The above drawbacks may be overcome to some extent if a two bed pyrolysis system is utilized wherein a pyrolysis fluidized bed and an incineration fluidized bed are parallely arranged between which two inclined conduits are disposed so as to circulate particles or grains between the two beds through the conduits such that the necessary heat in the pyrolyzing bed for maintaining the pyrolysis process is supplied by the above-noted circulation. In this system, the generated pyrolysis gas will not be diluted by the exhaust gas whereby pyrolysis gas having a high calorie content is obtained and, further regeneration of the grains is effectively and automatically performed during the circulation of the grains within the system. Therefore, the two bed process above is considered to be a very efficient system.
However, in order to make the transfer of the grains in the conduits of the two bed system smooth, it is necessary to dispose the conduits steeply, with an angle of inclination greater than the angle of repose for the grains and this makes it necessary to increase the height of the fluidized bed. Accordingly, the total height of the apparatus becomes great and this may increase the installation expense and, further, the operation becomes complex and troublesome.
Further, it is difficult to induce or maintain smooth fluidizing as the fluidized bed becomes higher. On the other hand, in case municipal waste is charged into the pyrolyzing apparatus, it is necessary to remove non-organic residue such as glass and metals. Therefore, if the two bed pyrolysis system is utilized, two discharge openings are generally required to remove such residue. In this case the device and the operation required for removing the residue at two places become troublesome and complex.
Further, removal of such residue is a dangerous operation, particularly in case from the pyrolyzing bed section since leaking of the pyrolysis gas generated by pyrolyzing or injected into the bed for fluidization creates the possibility of fire and/or explosion and, thus, provision of a safety device at each of such discharge openings is mandatory for the sake of safety. Therefore, removal of such residue at more than one place is not recommended.